System and method for operating a cooling loop

ABSTRACT

A system for operating a cooling loop associated with a space and including at least one cooling coil and cooling fluid supply, the system including: a grain sensor positioned with respect to the space and providing a value indicative of the amount of moisture in the space; at least one pump fluidly coupled across the coil; at least one flow limiter fluidly coupled to the coil and limiting a flow of cooling fluid between the cooling fluid supply and the coil; and at least one controller electrically coupled to the flow limiter; wherein, the at least one controller selectively operates the flow limiter responsive to the value indicative of the amount of moisture in the space and the pump re-circulates cooling fluid independent of the cooling fluid supply dependently upon the flow limiter.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. patent application Ser. No. 12/315,190,filed Nov. 8, 2009, entitled “System and Method for Operating a CoolingLoop”, which claims priority to U.S. Provisional Patent Application No.61/004,523, filed Nov. 28, 2007, entitled “System and Method forOperating a Cooling Loop”, the entireties of which are expresslyincorporated herein by reference.

BACKGROUND Field of the Invention

The present invention relates generally to heating and cooling systems,and more particularly to heating and cooling systems incorporating acooling coil and their operation.

BRIEF DESCRIPTION OF THE FIGURES

Understanding of the present invention will be facilitated byconsideration of the following detailed description of the preferredembodiments of the present invention taken in conjunction with theaccompanying drawings, in which like numerals refer to like parts and inwhich:

FIG. 1 illustrates a schematic representation of a system incorporatinga cooling coil;

FIG. 2 illustrates a schematic representation of a system incorporatinga cooling coil according to an embodiment of the present invention; and

FIG. 3 illustrates a schematic representation of a system incorporatinga cooling coil according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

It is to be understood that the figures and descriptions of the presentinvention have been simplified to illustrate elements that are relevantfor a clear understanding of the present invention, while eliminating,for purposes of clarity, many other elements found in typical heatingand cooling systems. However, because such elements are well known inthe art, and because they do not facilitate a better understanding ofthe present invention, a discussion of such elements is not providedherein. The disclosure herein is directed to all such variations andmodifications known to those skilled in the art.

FIG. 1 shows a schematic representation of a chilled water system 10.System 10 receives chilled water via a supply line 12, and returns waterthat has been used to cool air 14 via line 16. Chilled water supply line12 and chilled water return line 16 are interconnected via cooling coil18. Basically, chilled water is supplied to system 10 via supply line12. Supplied chilled water circulates through coil 18, where anair/water heat exchange occurs, leading to air 18 forced through coil 14being cooled and the supplied chilled water being warmed. The warmedchilled water from coil 18 is returned for re-chilling by line 16.Chilled air 14 may be supplied to a space 30, such as a conventionalspace within a building serviced by system 10. Chilled water supply andreturn lines, and cooling coils, are well known to those possessing anordinary skill in the pertinent arts.

Water flow through coil 18 is controlled via valve 20. While valve 20 isshown to be in line 14, it may be analogously situated in line 12.Either way, valve 20 may be used to throttle chilled water flow throughcoil 18, thereby controlling the cooling of air 14. The position ofvalve 20, and hence amount of cooling provided to air 14, is controlledby temperature controller 24, which is responsive to a conventionalcontrol algorithm (e.g., proportional-integral, or proportional-integral-derivative) and a temperature transmitter or sensor 22 andsetpoint supplied by a setpoint generator 28. Temperature transmitter 22provides a signal indicative of the temperature of air 14 after coolingby coil 18. Setpoint generator 28 provides a signal or value indicativeof a temperature setpoint responsively to a percent relative humiditysensor 26. Sensor 26 provides a signal indicative of the percentrelative humidity of space 30.

Controller 24 compares the temperature of air 14 to the setpoint, andmodulates the position of valve 20 accordingly. In essence, if air 14 istoo warm, valve 20 may be opened to provide more chilled water throughcoil 18, thereby providing more cooling. If air 14 is too cold, valve 20may be partially closed, to provide less chilled water through coil 18,thereby providing less cooling. By way of non-limiting example only, atypical setpoint for air 14 temperature may be around 52 degreesFahrenheit to around 58 degrees Fahrenheit, depending upon the relativehumidity of space 30 and operator preference. Air 14 may be reheatedprior to introduction to space 30, to around 70 degrees Fahrenheit toaround 72 degrees Fahrenheit, depending upon operator preference.

Such a configuration may be subject to certain shortcomings. Forexample, as chilled water flow through coil 18 lessens, flow may becomelaminar in nature. In such an event, heat exchange with air 14 maybecome significantly reduced, and a threshold condition effected betweenwhere proper air 14 cooling does and doesn't occur. This leads toinefficient cycling of system 10.

Referring now to FIG. 2, there is shown a schematic representation of asystem 100 according to an embodiment of the present invention. Likeelements in FIGS. 1 and 2 have been labeled with like reference fornon-limiting sake of explanation.

System 100 additionally includes a coil re-circulating line 105. Whileline 105 is shown in conjunction with a single coil 18, it mayanalogously be coupled across a plurality of cooling coils, for example.Either way, recirculating line 105 connects chilled water return line 16to chilled water supply line 12. In the illustrated embodiment of FIG.2, recirculating line 105 connects to return line 116 upstream fromvalve 20.

In the embodiment of FIG. 2, recirculating line 105 includes a seriallycoupled pump 110 and check valve 120. Pump 110 serves to reintroducewarmed chilled water from coil 18 return line 14 to supply line 12, andcoil 18. Pump 110 operates responsively to variable frequency drive(VFD) 130. Pump 110 and drive 130 may, in certain embodiments, beselected to provide around 120% of the full- load, design coil flow ofcoil 18. Check valve 120 serves to prevent chilled water from supplyline 12 bypassing coil 18.

For non-limiting purposes of explanation only, it should be understoodthat cooling coils have a design temperature differential (ΔT_(design))between the chilled water supply line 12 and chilled water return line16. The ΔT_(design) of a cooling coil is function of the original designof the entire chilled water system. An exemplary ΔT_(design) of acooling coil may be around 10 degrees Fahrenheit to around 15 degreesFahrenheit. Coil 18 operates efficiently (e.g., may be characterized asefficiently exchanging heat between chilled water and air) atΔT_(design). As the actual temperature differential across a coolingcoil (ΔT_(actual)) varies from ΔT_(design) though, the coil efficiencymay degrade. This may result from a number of factors, including theoccurrence of laminar flow through coil 18, for example.

Referring still to FIG. 2, system 100 also includes temperaturetransmitters or sensors 140, 150. Temperature transmitters 140, 150 maytake the form of commercially available platinum tip resistancetemperature detectors (RTD's), for example. Temperature transmitter 140provides a signal indicative of the temperature of water in chilledwater return line 16, after passing through cooling coil 18. Temperaturetransmitter 150 provides a signal indicative of the temperature of waterin chilled water supply line 12, prior to passing through cooling coil18. While temperature transmitter 150 is shown in the embodiment of FIG.2 downstream from recirculating line 105, it may optionally bepositioned upstream from recirculating line 105 in supply line 12.

System 100 also includes a temperature controller 160 coupled totemperature transmitters 140, 150. Controller 160 determines an actualtemperature differential ΔT_(actual) across coil 18 and compares it toΔT_(design) of coil 18. Where controller 160 determinesΔT_(actual)<ΔT_(design), it may signal VFD 130 to slow pump 110.Conversely, where controller 160 determines ΔT_(actual)>ΔT_(design), itmay signal VFD 130 to speed pump 110. In certain embodiments, controller160 may take the form of a commercially available, digitalproportional-integral controller.

Referring still to FIG. 2, system 200 also includes a space sensor 170.Space sensor 170 detects the relative humidity of space 30 (analogouslyto sensor 26), and additionally the temperature of space 30. Spacesensor 170 is coupled to a grain controller 180.

Grain controller 180 serves to calculate the absolute humidity in space30 responsively to sensor 170, such as by using a conventionalpsychometric-based approach. The absolute humidity may be expressed ingrains of moisture/pound of dry air, for example. Regardless, graincontroller 180 utilizes the determined absolute humidity of space 30,together with a predetermined desired absolute humidity, to establish asetpoint for controller 24. By way of non-limiting example, the desiredabsolute humidity may be around 64.5 grains of moisture/pound of dryair. Where the controller 180 determined absolute humidity is greaterthan 64.5 grains of moisture/pound of dry air, it may increase thetemperature setpoint of controller 24. Analogously, where the controller180 determined absolute humidity is less than 64.5 grains ofmoisture/pound of dry air, it may decrease the temperature setpoint ofcontroller 24. As will be understood by those possessing an ordinaryskill in the pertinent arts, the absolute humidity of space 30 istemperature independent, whereas the relative humidity of space 30utilized in system 10 to determine a setpoint is temperature dependent.

In certain embodiments of the present invention, space sensor 170 maytake the form of a temperature and humidity transmitter, such as thosecommercially available via Rotronic Instrument Corp., of Huntingdon,N.Y., and controller 180 may take the form of a commercially available,digital proportional-integral controller.

Controller 24 may throttle valve 20 in a manner analogous to system 10responsively to air 14 temperature as determined by sensor 14 and thesetpoint provided by grain controller 180. In certain embodiments of thepresent invention, temperature transmitter 22 may take the form of acommercially available platinum tip RTD's, and controller 24 may takethe form of a commercially available, digital proportional-integralcontroller.

Referring now to FIG. 3, there is shown a schematic representation of asystem 200 according to an embodiment of the present invention. Likeelements in FIGS. 1, 2 and 3 have been labeled with like reference fornon-limiting sake of explanation.

Different from the embodiment of FIG. 2, system 200 includes anadditional valve 210. Controller 160 throttles flow throughrecirculating line 105 to achieve a similar result as the embodiment ofFIG. 2.

It will be apparent to those skilled in the art that modifications andvariations may be made without departing from the spirit or scope of theinvention.

What is claimed is:
 1. A system for operating a cooling loop associatedwith a space and including at least one cooling coil and cooling fluidsupply, the system comprising: a grain sensor positioned with respect tothe space and providing a value indicative of the amount of moisture inthe space; at least one pump fluidly coupled across the coil; at leastone flow limiter fluidly coupled to the coil and limiting a low ofcooling fluid between the cooling fluid supply and the coil; and atleast one controller electrically coupled to the flow limiter; wherein,the at least one controller selectively operates the flow limiterresponsive to the value indicative of the amount of moisture in thespace and the pump re-circulates cooling fluid independent of thecooling fluid supply dependently upon the flow limiter.
 2. The system ofclaim 1, further comprising a variable drive electrically coupled to theat least one pump, wherein the pump is variably operable responsive tothe variable drive, the drive is electrically coupled to the at leastone controller, and the pump operates at a speed substantially inverselyrelated to value indicative of the amount of moisture in the space. 3.The system of claim 1, further including at least one temperature sensorpositioned with respect to the coil and providing a value indicative thetemperature of the cooling fluid entering the coil, and beingelectrically coupled to the at least one controller.
 4. The system ofclaim 1, further including at least one temperature sensor positionedwith respect to the coil and providing a value indicative thetemperature of the cooling fluid exiting the coil, and beingelectrically coupled to the at least one controller.
 5. The method ofclaim 1, further comprising: a first temperature sensor positioned withrespect to the coil and providing a value indicative the temperature ofthe cooling fluid entering the coil, and being electrically coupled tothe at least one controller. a second temperature sensor positioned withrespect to the coil and providing a value indicative the temperature ofthe cooling fluid exiting the coil, and being electrically coupled tothe at least one controller. wherein, the pump re-circulates coolingfluid independent of the cooling fluid supply dependently upon the flowlimiter and the first and second temperature sensors.
 6. The system ofclaim 1, further including at least one temperature sensor positionedwith respect to the coil and providing a value indicative thetemperature of air exiting the coil, and being electrically coupled tothe at least one controller.
 7. The system of claim 1, wherein the atleast one controller selectively operates the flow limiter responsive tothe value indicative of the amount of moisture in the space and thevalue indicative the temperature of air existing the coil.
 8. A methodfor operating a cooling loop associated with a space and including atleast one cooling coil and cooling fluid supply, the method comprising:determining a value substantially indicative of the absolute humidity ofthe space; selectively recirculating cooling fluid through the at leastone coil and independently of the supply dependently upon the determinedvalue substantially indicative of the absolute humidity of the space. 9.The method of claim 8, further comprising selectively operating avariable speed pump that recirculates the cooling fluid dependently upontemperatures of cooling fluid entering and existing the at least onecoil.
 10. The method of claim 8, further comprising determining a valuesubstantially indicative of a value indicative the temperature of airexiting the coil, and selectively recirculating cooling fluid throughthe at least one coil and independently of the supply dependently uponthe determined value substantially indicative of the absolute humidityof the space and the determined value substantially indicative of avalue indicative the temperature of air exiting the coil.